The present invention relates to mechanisms for minimizing frost buildup around the frame of an opening in a refrigerated display case, especially those having doors covering such openings.
In display refrigerators having doors which render access to the interior portion for customers, condensation near the door openings will accumulate and freeze forming frost at the joints. This typically occurs because the cabinet door will approach the temperature of the refrigeration air used in maintaining the goods on display in a frozen or refrigerated state. As a result, portions of the refrigerator door will reach a temperature well below that of the ambient air effecting condensation and possibly cause freezing of the moisture carried by the ambient air. The frozen moisture can build up to such an extent that the door will jamb thereby impairing the ability of the customer to get to the goods he wishes to purchase. In addition, it creates a rather unsightly appearance detracting from the cleanliness and sanitation environment which the retail users of such refrigeration cabinets desire to achieve. This problem is especially prevalent in the operation of refrigerated display cases having sliding type doors.
Although attempts have been made to prevent the buildup of condensation on the frame of the refrigerator, they are largely inefficient and very wasteful. An example of such an attempt is the U.S. Pat. No. 2,535,278 to Fletcher. The device illustrated in the Fletcher patent relates to the style of refrigerator which is heated by light that forms part of a warning system. The light generates heat which serves to warm the exposed surface of the case by conduction through a metal surface. In addition, the heat generated to a lesser extent warms the ambient air which rises in a channel to assist in warming the exposed surface of the case.
A similar example of such attempts to eliminate this formation of condensate includes U.S. Pat. No. 3,135,100 to Taylor et al. which discloses electrical means mounted on the door of a refrigerator to heat the door and thereby prevent the formation of condensation and frost. A transformer is included to limit the amount of voltage which is used to generate the electric current and ultimately the heat in the electrical wires. Other examples of refrigerated enclosures incorporating heating elements in the form of electrical resistance heaters include U.S. Pat. Nos. 2,858,408 to Barroero, 3,449,925 to Barroero, and 3,869,873 to Thomas. In another type of system, the heat from the refrigerant passing through the liquid lines has been used for minimizing frost in the grille covering the air inlet opening of the air conduit of a refrigerated display case; see U.S. Pat. No. 3,371,503 to Perez.
The problem which is characteristic of many of the approaches of the past is the failure to effectively use the heat generated by items which are already typically used on refrigerators for other purposes to prevent the buildup of condensation at the joints of the door and the frame. Where resistance wires have been relied upon as a sole source of heat there results an inefficiency because of the added heat to the refrigerating case which must be cooled by the refrigeration system as well as the cost of the electrical power needed to provide the electrical heating wires with current. In addition, other sources of heat have simply not been efficient in and of themselves to prevent the formation of the condensation.